Digital image system for photographing photos and/or filming videos has become an essential portion in modern electronic device, such as smart phone, mobile phone, handheld computer, portable computer, tabular computer, notebook computer, wearable gadget (e.g., glasses or watch), navigator, digital camera, network camera (e.g., IP camera), digital camcorder, game console, interactive toy and surveillance system, etc.
In modern digital image system, image acquisition is typically implemented by rolling shutter which controls exposure to an image sensor. The image sensor may include a plurality of pixel sensors arranged in an array; for pixel sensors arranged in a same line (e.g., a horizontal scan line, a row), light data picked up by each pixel sensor of the line may be sequentially read out during a readout interval. With rolling shutter mechanism, the readout intervals of different lines (rows) are arranged to happen sequentially, rather than concurrently, so the image sensor may be prevented from collecting excessive photons during each readout interval even though there is no physical light-shielding, and thus reduce cost of the image sensor. However, the rolling shutter also introduces a number of artifacts due to the sequential row (line) capturing and readout, and one of the artifacts is illumination flicker caused by fluctuating light source.
Therefore, there is a need for detecting and removing the illumination flicker noise of images.